Alkoxy silyl capping agents for making terminally functionalized polymers

ABSTRACT

The capping of anionic polymers to make functionalized polymers is improved by using alkoxy silyl compounds having protected functional groups, such as acetal groups, as the capping agent. The protected functional groups are stable under a variety of conditions and then readily convert to more reactive terminal functional groups useful for making adhesives, sealants and coatings.

FIELD OF THE INVENTION

This invention relates to preparation of functionalized polymers used ascomponents in adhesives, sealants and coatings. More specifically, thisinvention relates to capping of living anionic polymers to add terminalfunctional groups.

BACKGROUND OF THE INVENTION

Anionic polymerization of conjugated dienes with lithium initiators,such as sec-butyllithium, and hydrogenation of residual unsaturation hasbeen described in many references. The capping of mono-initiated anddi-initiated living anionic polymers to form functional end groups isdescribed in U.S. patent application Ser. No. 938,917 filed Aug. 31,1992 (T3229).

Anionic polymerization using protected functional initiators having thestructure R¹ R² R³ Si-O-A'-Li is described in U.S. No. 5,331,058 whereinR¹, R², and R³ are preferably alkyl, alkoxy, aryl, or alkaryl groupshaving from 1 to 10 carbon atoms, and A' is preferably a branched orstraight chain bridging group having at least 2 carbon atoms.Polymerization with such a protected functional initiator, followed bycapping to produce a second terminal functional group, producestelechelic polymers which otherwise can be prepared by capping polymersprepared with difunctional initiators such as 1,4 dilithiobutane andlithium naphthalide. The use of a protected functional group avoids theformation of ionic gels which occur when diinitiated polymers are cappedwith reagents such as ethylene oxide. These gels form even in relativelypolar solvent mixtures and hinder subsequent processing steps.

One way to prepare difunctional telechelic polymers without forming agel is to use a protected functional initiator such as the structure:##STR1## wherein A" is cyclohexyl or -CR'R"-, wherein R' is a linearalkyl having from 1 to 10 carbon atoms and R" is hydrogen or a linearalkyl having from 1 to 10 carbon atoms. The compounds of structure (A)initiate polymerization of anionic polymers at high polymerizationtemperatures. The protected functional group survives hydrogenation ofconjugated diene polymers and is readily removed by hydrolysis in thepresence of methanesulfonic acid. The initiators of structure (A) can beused to make telechelic polymers by capping with ethylene oxide oroxetane. However, oxetane is not readily available on a commercial scaleand ethylene oxide can be hazardous due to its reactivity and toxicity.

A recent publication by M. A. Peters and J. M. DeSimone (Polym. Prepr.(Am. Chem. Soc. Div. Polym. Chem.), 1994,35(2), 484) describes thepreparation of mono- and di-functional polymers by cappingmono-initiated and di-initiated living anionic polymers with achlorosilane of the following structure: ##STR2## instead of ethyleneoxide or oxetane. In this process, LiC1 is eliminated and the protectedalcohol group is added to the polymer chain end, avoiding gel formation.

SUMMARY OF THE INVENTION

The present invention is the discovery that mono-initiated ordi-initiated anionic polymers are efficiently capped with silyl alkoxycompounds possessing acidic alkoxy radicals as leaving groups and avariety of protected functional groups, resulting in terminal protectedfunctional groups that are stable under a variety of conditions. Theprotected functional group is preferably an acetal group, but can be anygroup that readily converts to more reactive terminal functional groupsuseful for making adhesives, sealants and coatings.

DETAILED DESCRIPTION OF THE INVENTION

The anionic polymerization of unsaturated monomers with mono-lithiuminitiators such as s-butyllithium or di-lithium initiators such as thediadduct of s-butyllithium and m-diisopropenylbenzene is described inU.S. patent application Ser. No. 938,917 filed Aug. 31, 1992 (T3229)which description is incorporated by reference herein. Polymerizationresults in one or more terminal lithium atoms which readily react withethylene oxide or oxetane to cap the polymers with one or more terminalhydroxyl groups per molecule. The terminal hydroxyl groups tend to formweak associations between molecules, which has no adverse effects ifthese chains are mono-initiated. However, the di-alkoxide polymer anionsformed by capping di-initiated polymers associate to form an ionic gelwhich is very difficult to process.

The use of the protected-functional capping agent of structure (B)avoids gel formation and avoids the problems presented by capping withcyclic ethers. However, the use of this reagent to cap low molecularweight polymer anions results in the generation of large amounts oflithium chloride, which introduces new difficulties. For example, thepreferred method for converting the silyl ether to the alcohol involvescontact with aqueous methanesulfonic acid. The presence of high levelsof halide in such a mixture presents severe corrosion problems. Also,the polymers are preferably hydrogenated with a Ni/A1 catalyst (to bedescribed in detail below) that is poisoned by high levels of halide. Inorder to hydrogenate polymers capped with structure (B), an aqueous acidwash would likely be required to remove the LiC1. A drying step wouldprobably also be required, since the catalyst is also deactivated bywater.

The advantages gained by using a protected-functional capping agent arerealized without introducing halide ions by capping mono-initiated ordi-initiated polymers with silyl alkoxides having acidic alkoxy leavinggroups and stable protecting groups as shown by the following structure:##STR3## wherein Y is a protected functional group, preferably an acetalgroup, which is stable during the polymerization step and converts tomore reactive terminal functionality as described below, and Z is anacidic alkoxy group, preferably phenoxy radicals or trifluoroethoxyradicals. The acetal group is preferred as the protecting group since itis easily introduced and cleaved, and has more favorable raw materialcosts than the t-butyl dimethylsilyl ether group of structure (B) or thetrimethylsilyl ether group of structure (A).

The alkoxy silyl capping agents of equation (1) are prepared byhydrosilation of the appropriate dimethylsilane (Z-Si(CH₃)₂ H) with anallyl species containing the protected functional group (CH₂ =CH-CH₂-y). Hydrosilation was accomplished using a Pt catalyst, as is generallydescribed by M. A. Peters and J. M. DeSimone (Polym. Prepr. (Am. Chem.Soc. Div. Polym. Chem.), 1994,35(2), 484). After capping of the polymer,the protecting group is removed by reaction with methanesulfonic acid,as described in U.S. patent application No. 155,665 filed Nov. 22, 1993(TH0010) which disclosure is incorporated by reference herein.

A variety of processes for removal of the protecting groups are known;for a review, see T. W. Greene, "Protective Groups in OrganicSynthesis", J. Wiley and Sons, New York, 1981, incorporated herein byreference. A preferable process would involve easily handled, relativelylow toxicity, and inexpensive reagents. In a preferred process, theacetal group is removed by reaction of the polymer solution with 1-10equivalents (basis acetal end groups) of a strong organic acid,preferably methanesulfonic acid (MSA), in the presence of 0.1% -2% byweight of water and 5% -50% by volume of isopropanol (IPA) at about 50°C.

Mono-initiation is preferentially performed using s-butyllithium.Di-initiation is preferentially performed using the diadduct ofs-butyllithium and m-diisopropenylbenzene, as described in U.S. patentapplication Ser. No. 938,917 filed Aug. 31, 1992 (T3229) which isincorporated by reference herein. Polymerization is preferably initiatedat a temperature from 20° C. to 60° C., most preferably from 30° C. to40° C. It is generally advisable to keep the polymerization temperaturebelow about 100° C.; above this temperature, side reactions that changemicrostructure and limit capping efficiency may become important.Polymerizations can be carried out over a range of solids, preferablyfrom about 5% to about 80%, most preferably from about 10% to about 40%.For high solids polymerizations, it is preferable to add the monomer inincrements to avoid exceeding the desired polymerization temperature. Ifthe initiator is to be added to the full monomer charge, it ispreferable to run the polymerization between 10% and 20% solids.

The protected group is introduced by reacting 1.05-2 equivalents of thecapping agent of structure (1) per lithium site (2 per chain in the caseof di-initiated polymers) at a temperature of 40°-80° C. for at least 30minutes. If no polar microstructure modifier was present during thepolymerization, it may be desirable to add a non-reactive coordinatingagent, such as diethyl ether or glyme, during this step.

The polymers of the present invention preferably comprise a polymerizedunsaturated monomer selected from the groups consisting of styrene,1,3-butadiene, and isoprene. When the anionic polymer comprisespolymerized 1,3-butadiene which contains residual monomer unsaturationwhich is to be saturated by hydrogenation, the anionic polymerization ofthe conjugated diene hydrocarbons is typically controlled with structuremodifiers such as diethyl ether or glyme (1,2-diethoxyethane) to obtainthe desired amount of 1,4-addition. As described in Re 27,145 which isincorporated by reference herein, the level of 1,2-addition of abutadiene polymer or copolymer can greatly affect elastomeric propertiesafter hydrogenation. The hydrogenated polymers exhibit improved heatstability and weatherability in the final, adhesive, sealant or coating.

The 1,2-addition of 1,3-butadiene polymers having terminal functionalgroups influences the viscosity of the polymers as described in moredetail below. A 1,2-addition of about 40% is achieved duringpolymerization at 50° C. with about 6% by volume of diethyl ether orabout 1000 ppm of glyme. Generally, vinyl contents in this range aredesirable if the product is to be hydrogenated, while low vinyl contentsare preferred if the polymer is to be used in its unsaturated form.

Hydrogenation of at least 90%, preferably at least 95%, of theunsaturation in low molecular weight butadiene polymers is achieved withnickel catalysts as described in U.S. Patents Re. 27,145 and 4,970,254and U.S. patent application Ser. No. 07/785715 which are incorporated byreference herein. The preferred nickel catalyst is a mixture of nickel2-ethylhexanoate and triethylaluminum described in more detail in theexamples. It is preferable to extract the nickel catalyst afterhydrogenation by stirring the polymer solution with aqueous phosphoricacid (20-30 percent by weight), at a volume ratio of about 0.5 partsaqueous acid to 1 part polymer solution, at about 50° C. for 30-60minutes while sparging with a mixture of oxygen in nitrogen. This stepis also described in more detail in the examples.

Sufficient IPA must be present during deprotection to prevent theformation of a discrete aqueous phase. Excess acid is then removed bywashing with dilute aqueous base, preferably 0.1N -0.5N sodiumhydroxide, followed by water. For some applications, such as coatingsprepared by baked cures of the polymer with amino resins in the presenceof a strong organic acid catalyst, it may be preferable to use thepolymer in its "protected" form. The viscosity of the protected polymeris lower and conditions such as those described above should accomplishthe deprotection (generate the alcohol) during the cure.

The conjugated diene polymers produced as described above have theconventional utilities for terminally functionalized polymers of such asforming adhesives, coatings, and sealants. Additionally, the polymersmay be used to modify polyurethanes, polyesters, polyamides,polycarbonates, and epoxy resins.

A composition of the instant invention may contain plasticizers, such asrubber extending plasticizers, or compounding oils or organic orinorganic pigments and dyes. Rubber compounding oils are well-known inthe art and include both high saturates content oils and high aromaticscontent oils. Preferred plasticizers are highly saturated oils, e.g.Tufflo® 6056 and 6204 oil made by Arco and process oils, e.g. Shellflex®371 oil made by Shell. The amounts of rubber compounding oil employed inthe invention composition can vary from 0 to about 500 phr, preferablybetween about 0 to about 100 phr, and most preferably between about 0and about 60 phr.

Optional components of the present invention are stabilizers whichinhibit or retard heat degradation, oxidation, skin formation and colorformation. Stabilizers are typically added to the commercially availablecompounds in order to protect the polymers against heat degradation andoxidation during the preparation, use and high temperature storage ofthe composition.

Various types of fillers and pigments can be included in the coating orsealant formulation. This is especially true for exterior coatings orsealants in which fillers are added not only to create the desiredappeal but also to improve the performance of the coatings or sealantsuch as its weather-ability. A wide variety of fillers can be used.Suitable fillers include calcium carbonate, clays, talcs, silica, zincoxide, titanium dioxide and the like. The amount of filler usually is inthe range of 0 to about 65% w based on the solvent free portion of theformulation depending on the type of filler used and the application forwhich the coating or sealant is intended. An especially preferred filleris titanium dioxide.

The dihydroxylated conjugated diene polymers of the present inventionmay also be blended with other polymers to improve their impact strengthand/or flexibility. Such polymers are generally condensation polymersincluding polyamides, polyurethanes, vinyl alcohol polymers, vinyl esterpolymers, polysulfones, polycarbonates and polyesters, including those,like polyacetones, which have a recurring ester linkage in the molecule,and those, like polyalkylene arylates, including polyalkyleneterephthalates, having a structure formed by polycondensation of adicarboxylic acid with a glycol. The blends may be made in the reactoror in a post compounding step.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The preferred process of the present invention caps di-initiated1,3-butadiene polymers with alkoxy silyl capping agents having acetalprotecting groups represented by the structure: ##STR4## wherein Z' is aphenoxy group or a trifluoroethoxy group. The alkoxy silyl cappingagents of equation (2) are prepared by hydrosilation of the appropriatedimethylsilane (Z-Si(CH₃)₂ H) with the vinyl acetal resulting from thereaction of ethyl vinyl ether and allyl alcohol in the presence of anacid catalyst. Hydrosilation was accomplished using a Pt catalyst, as isgenerally described by M. A. Peters and J. M. DeSimone (Polym. Prepr.(Am. Chem. Soc. Div. Polym. Chem.), 1994,35(2), 484). After capping ofthe polymer, the protecting group is removed by reaction withmethanesulfonic acid, as described in U.S. patent application No.155,665 filed Nov. 22, 1993 (TH0010) which disclosure is incorporated byreference herein.

The preferred process ultimately produces dihydroxylated, saturated1,3-butadiene polymers having a peak molecular weight from 500 to200,000, most preferably from 500 to 20,000. The dihydroxylated polymerscan be unsaturated with 1,2-addition from 5% to 95% or hydrogenated with1,2-addition from 30% to 70%. The polymers preferably have from 1.75 to2.0, most preferably from 1.95 to 2.0, terminal hydroxyl groups permolecule.

The preferred process initially makes a novel intermediate polymer whichhas a protected acetal functional group on each end of a linear1,3-butadiene polymer. The intermediate polymer can be sold in asaturated or unsaturated version for making adhesives, sealants, andcoatings wherein either the supplier or the customer deprotects thefunctional groups by a reaction that converts the protected functionalgroups to hydroxyl groups.

The preferred process comprises di-initiation with the diadduct ofs-butyllithium and m-diisopropenylbenzene, polymerization of1,3-butadiene, and capping with an acidic alkoxy silyl acetal havingstructure (2). The reaction results in exclusion of lithium alkoxide andthe silyl acetal protecting group replaces the lithium at both ends ofthe living anionic polymer molecule.

The intermediate polymers of the present invention are useful for makingadhesives (including pressure sensitive adhesives, contact adhesives,laminating adhesives and assembly adhesives), sealants (such as urethanearchitectural sealants, etc.), coatings (such as topcoats forautomotive, epoxy primers for metal, polyester coil coatings, alkydmaintenance coatings, etc.), films (such as those requiring heat andsolvent resistance), molded and extruded thermoplastic and thermosetparts (for example thermoplastic injection molded polyurethane rollersor reaction injection molded thermoset auto bumper, facie, etc.).

The present invention is further described by the following exampleswhich include the best mode known to Applicant for making a saturated,linear polybutadiene polymer having one or two terminal silyl acetalgroups. The examples are not intended to limit the present invention tospecific embodiments although each example may support a separate claimwhich Applicant asserts to be a patentable invention.

EXAMPLES

The peak molecular weights were measured using gel permeationchromatography (GPC) calibrated with polybutadiene standards havingknown peak molecular weights. The solvent for the GPC analyses wastetrahydrofuran.

The 1,2-additions of polybutadiene were measured by ¹³ C NMR inchloroform solution.

Three protected-functional capping agents,ethyl(dimethylethoxysilylpropyl) formaldehyde acetal (CA1),ethyl(dimethylphenoxysilylpropyl) formaldehyde acetal (CA2), andethyl(dimethyl-3,3,3-trifluoroethoxysilylpropyl) formaldehyde acetal(CA3), were prepared by hydrosilation of the appropriate dimethylsilane(dimethylethoxysilane, dimethylphenoxysilane, anddimethyl-3,3,3-trifluoroethoxysilane, respectively) as describedpreviously. Reaction conditions are summarized in Table 1 for theseagents.

Example 1

Poly(butadiene) "mono-ols" were prepared by initiation withs-butyllithium while poly(butadiene) "diols" were prepared by initiationwith the product of diisopropenyl benzene and 2 equivalents ofs-butyllithium. Unless otherwise specified, polymer examples 1-1 through3-2 were prepared in cyclohexane/diethyl ether(10%) and methanol wasadded to terminate any uncapped chains. For the alkoxy silyl acetalcapping agents of structure (2) (i.e. CA1, CA2, and CA3), thecharacteristic yellow color of the polymer anion faded considerablyafter adding the capping agent. Samples were deprotected usingmethanesulfonic acid, dried (rotary evaporator), and analyzed by GPC, ¹³C NMR, and HPLC. Samples taken prior to deprotection were contacted withconcentrated phosphoric acid to remove or neutralize lithium salts priorto drying; except in one case, described below, this did not result insignificant hydrolysis of the acetal groups.

To simplify the analysis, screening studies were carried out using"mono-initiated" polymers although diinitiated polymers are preferred.The results are summarized in Table 2. HPLC could not unambiguouslyresolve acetal-capped polymer from proton-terminated polymer, so onlyNMR data was used to assess the capping efficiency prior todeprotection. The results of the analysis of the deprotected productsare also summarized in Table 2; ¹³ C NMR results are consistent withquantitative hydrolysis of the acetal group. The more acidic alkoxycapping agents were much more reactive than the ethoxy analog, yieldingcapping efficiencies on the order of 90% without adding THF or any otherreaction promoter.

GPC analysis indicated that a small fraction of the polymer anions werecoupled (twice original MW). This may be due to oxygen coupling or thepresence of a small amount of silane impurity with two "active" ligands;the capping agents were added without further purification. Theseexperiments also suggest that both capping agents react readily atmoderate temperatures. Analysis by NMR could detect no significantimprovement in capping efficiency between samples capped for 30 minutesat 40° C. and samples taken after heating to 80° C. and holding at 80°C. for an hour.

EXAMPLE 2

In order to assess the utility of this approach for preparing diols, adiinitiated butadiene polymer (Example 2-1) was capped with the phenoxysilyl acetal compound (CA2) at 40° C., and an aliquot of the same cementwas reacted with excess ethylene oxide (Example 2-2). The analyticalresults are summarized in Table 3. The silyl acetal capped productremained a viscous liquid while the ethylene oxide capped product formeda gel. After deprotection, the silyl acetal capped product was analyzedby HPLC as well as ¹³ C NMR. The NMR results indicate slightly highercapping efficiency with the phenoxy silyl acetal than with ethyleneoxide. The HPLC chromatograms are consistent with this conclusion. Theethylene oxide capped product contains substantially moreunfunctionalized and mono-functionalized material and less diol. Asubstantial amount of material, tentatively identified as tri-ol(resulting form initiation by trifunctional lithium species), was alsoobserved. The relatively high levels of both mono-ol and tri-ol in thispolymerization suggest that the optimum yield of diinitiator may nothave been achieved, but it is clear that products comparable to thoseobtained by EO capping were produced without the complications of thegel using the alkoxy silyl approach.

EXAMPLE 3

A sample (3-1) prepared by capping a monoinitiated polymer with thephenoxy silyl acetal compound (CA2), followed by methanol terminationwas hydrogenated using 300 ppm of a 2.5:1 Al:Ni catalyst, added in three100 ppm aliquots over 3 hours. About 95.6% of the polymer double bondswere hydrogenated. A sample of this cement was isolated without methanoladdition (3-2). Surprisingly, the acetal seems to have been hydrolyzedby the phosphoric acid neutralization; an unusually high level ofsuspended salts was also noted in the dry sample. On standing, asignificant amount of precipitate, presumably lithium phenoxide, settledout of the solution. After decanting from the precipitate, the samplewas hydrogenated as described above; the extent of hydrogenationachieved was quite low, only about 56%. The reason for the decreasedyield is unclear, but it seems safe to conclude that it is preferable toterminate with methanol prior to hydrogenation.

                  TABLE 1                                                         ______________________________________                                        Summary of Alkoxy Silyl Capping Reaction Conditions.                          Sample                                                                              Initiator CA #    CA:Li Rxn Time Rxn Temp                               ______________________________________                                        1-1   s-BuLi    CA1     1.5:1 60 min..sup.1                                                                          80° C..sup.1                    1-2   s-BuLi    CA1.sup.2                                                                             1.5:1 60 min..sup.1                                                                          80° C..sup.1                    1-3   s-BuLi    CA1.sup.3                                                                             1.5:1 60 min..sup.1                                                                          80° C..sup.1                    1-4   s-BuLi    CA2     1.5:1 30 min.  40° C.                          1-5   s-BuLi    CA2     1.5:1 60 min..sup.4                                                                          80° C.                          1-6   s-BuLi    CA3     1.5:1 30 min.  40° C.                          1-7   s-BuLi    CA3     1.5:1 60 min..sup.4                                                                          80° C.                          2-1   DiLi.sup.5                                                                              CA2     1.05:1                                                                              80 min.  40° C.                          3-1,3-2.sup.6                                                                       s-BuLi    CA3     1:1   60 min.  40° C.                          ______________________________________                                         .sup.1 CA added at 40° C., then heated to 80° C. for 60 min     .sup.2 100 ppm glyme added with CA1.                                          .sup.3 Tetrahydrofuran added until 5% by volume, prior to CA1.                .sup.4 Prepared by heating preceding 30 min/40° C. sample to           80° C. and holding for 60 min.                                         .sup.5 Product of 2 moles sbutylithium and 1 mole diisopropenyl benzene       (DIPB).                                                                       .sup.6 Sample 32 was not terminated with methanol.                       

                                      TABLE 2                                     __________________________________________________________________________    Summary of Analytical Data for Mono-ols Prepared by                           Capping with CA1 and CA2.                                                                 Capping  % hydrocarb.sup.1                                                                      % mono-ol.sup.1                                 Sample                                                                            MW (GPC)                                                                              Effic'y(NMR)                                                                           (NMR.sup.2 /HPLC)                                                                      (NMR.sup.3 /HPLC)                               __________________________________________________________________________    1-1 2,000   65%      40/34    60/66                                           1-2 5,000   70%      --       --                                              1-3 4,800   83%      28/15    72/85                                           1-4 --      94%      --       --                                              1-5 4,100.sup.4                                                                           99%      22/8     78/92                                           1-6 4,160.sup.4                                                                           89%      --       --                                              1-7 4,160.sup.4                                                                           90%      25/15    75/85                                           3-1 4,320.sup.4                                                                           80%      20.sup.5 /10.sup.5,6                                                                   80/90.sup.5,6                                   3-2 4,320.sup.4                                                                           79%      21.sup.5,7 /10.sup.5                                                                   79.sup.5,7 /90.sup.5                            __________________________________________________________________________     .sup.1 Unless otherwise specified, after deprotection.                        .sup.2 No acetal resonances detected by .sup.13 C NMR, consistent with        quantitative hydrolysis of all capped chains.                                 .sup.3 Lower value relative to HPLC and theoretical (complete conversion      of capped chains) may be due to error in backing out the contribution of      interefering resonances.                                                      .sup.4 2%-3% polymer of twice this MW (coupled product).                      .sup.5 Hydrogenated sample.                                                   .sup.6 Sample deprotected during isolation; did not require treatment wit     MSA/IPA to effect deprotection.                                               .sup.7 Capping efficiency prior to deprotection; hydrogenation obscures       sbu resonance so that the sbu:C--OH ratio cannot be determined.          

                                      TABLE 3                                     __________________________________________________________________________    Analytical Data for Diols Prepared by Capping with                            Phenoxy Silyl Acetal (CA2) or Ethylene Oxide (EO).                                Capping                                                                            MW   NMR  % HC % M-ol                                                                             % Diol                                                                             % Tri-ol                                    Sample                                                                            Agent                                                                              (GPC).sup.1                                                                        C.E. (HPLC)                                                                             (HPLC)                                                                             (HPLC)                                                                             (HPLC)                                      __________________________________________________________________________    2-1 CA2  4,700                                                                              96%  0.5  18   50   31.5                                        2-2 EO   4,500                                                                              86%  5    23.5 44.5 27                                          __________________________________________________________________________     .sup.1 MW of 4,400 prior to adding capping agent (MEOH termin.).         

We claim:
 1. A process for making functionalized polymers, comprisingthe steps of:anionically polymerizing an unsaturated monomer with amono-lithium or di-lithium initiator; and terminating the polymerizingstep by addition of an alkoxy silyl compound having the structure:##STR5## wherein Y is an acetal group, a t-butyl dimethylsilyl group, ora trimethylsilyl ether group, and Z is a phenoxy radical or atrifluoroethoxy radical.
 2. The process of claim 1, wherein thepolymerizing step is initiated with a di-lithium initiator at atemperature from 20° C. to 60° C.
 3. The process of claim 1, wherein theunsaturated monomer is selected from the groups consisting of styrene,1,3-butadiene, and isoprene.
 4. The process of claim 1, wherein Z is aphenoxy radical.
 5. The process of claim 4, wherein the unsaturatedmonomer is 1,3-butadiene.
 6. A process for making functionalizedpolymers, comprising the steps of:anionically polymerizing 1,3-butadienewith a monolithium or di-lithium initiator; and terminating thepolymerizing step by addition of an alkoxy silyl acetal compound havingthe structure: ##STR6## wherein Z' is a phenoxy radical or atrifluorethoxy radical.
 7. The process of claim 6, wherein thepolymerizing step is initiated with a di-lithium initiator at atemperature from 20° C. to 60° C.
 8. The process of claim 7, furthercomprising the step of hydrogenating residual unsaturation in thefunctionalized polymer.
 9. The process of claim 8, wherein Z' is aphenoxy radical.